The present invention relates to methods and apparatus for processing semiconductor wafers. More particularly, the present invention relates to methods and apparatus for improving byproduct particle control in a plasma processing chamber, thereby decreasing contamination and increasing the Mean Time Between Cleans (MTBC).
The use of plasma in processing semiconductor or glass substrates is known. In the manufacture of a semiconductor device or a flat panel display, for example, several steps involve plasma processing of a substrate. The plasma processing steps may include, for example, etching, deposition, and/or other plasma processing steps well known in the art. Some plasma processing steps produce byproduct chemical compounds which, if allowed to freely circulate within the plasma processing chamber, may cause contamination and concomitant defects in the finished product.
During plasma etching, for example, a plasma is typically created from reactant source gasses, which then react with the substrate surface to etch the desired pattern (using an appropriate photoresist or hard mask). As the reactive plasma species react with the surface of the substrate or with each other, byproducts are generated. A certain quantity of the byproducts, preferably most or all of it if possible, is exhausted away through an appropriate exhaust port of the plasma processing chamber.
Some of the byproducts, however, have a low volatility and may be deposited on inner surfaces of the plasma processing chamber. As processing continues, the byproduct deposition may build up and become a liability for particle generation. This happens when the byproduct film flakes off the chamber interior surfaces and becomes deposited as unwanted contaminants on the surface of the substrate undergoing processing. If deposited on the substrate surface, the byproduct particles may result in defects in the finished product, causing it to be rejected. For example, the deposition of unwanted particles on a substrate surface may cause electrical shorts between features which are intended to be electrically isolated from one another, or may undesirably mask areas targeted for etching. In a plasma-enhanced deposition step, the presence of unwanted contaminants on an underlying layer of a substrate may also prevent a subsequent layer from properly adhering to that underlying layer or undesirably altering the properties of the deposited film.
To keep the level of byproduct particles in a plasma processing chamber low, the chamber is opened from time to time and cleaned to remove the accumulated byproduct deposition. The frequency established for this cleaning is called the Mean Time Between Cleans (MTBC). If the deposited byproduct film flakes off readily from surfaces of the chamber interior, the Mean Time Between Cleans (MTBC) is disadvantageously shortened since a high level of contaminants may be reached in a relatively short period of time. The more frequent a plasma processing system has to be out of production for cleaning, the higher its cost of ownership, which in turn translates into higher expenses per unit produced.
In view of the foregoing, improved methods and apparatus for reducing the level of byproduct particle generation within a plasma processing chamber are desired. By reducing the level of byproduct particle generation, the contamination level within the plasma processing chamber may advantageously be maintained at an acceptable level for a longer period of time, thereby increasing the Mean Time Between Cleans (MTBC) and concomitantly reducing the system's cost of ownership.